Generally, a speedometer or a RPM(Revolutions Per Minute) meter is used to evaluate economic driving, which is considered as a standard for driving a vehicle. It is difficult to use the trip computer as a standard for improving fuel efficiency because a trip computer employed by some kinds of vehicles informs a driver of driving results obtained by computing a fuel consumption rate and a driving distance. Therefore, it causes fuel to be excessively lost, generates a large quantity of smoke, shortens the life span of the vehicle, and depreciates the performance of an engine of the vehicle.